I have two organisations, and can create repos within them, and push to these repos.
For any new organisations I create, I can make edits via GitHub.com, but when I try to push local changes I get:
remote: Permission to [new-org]/[new-repo].git denied to [user-name].
fatal: unable to access ‘https://github.com/[new-org]/[new-repo].git/’: The requested URL returned error: 403
I get the above issue if I try to push from command line or from SmartGit.
Pushing to repos from my existing organisations works fine in both cases.